History of Astronomy

1
History of Astronomy

• Chapter 2

2
Apparent motion of stars

• Rise from east, and set in the west.
• Rotate around Polaris.
• Any star rises 3 min 56 sec earlier every night.

3
Apparent motion of the Sun

• Sun follows the ecliptic.
• Ecliptic the path followed by the sun.

4
The celestial sphere ????? ????????

• Zenith The point directly overhead.

5
Sunrise and sunset
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Sunrise 28 Jan. 2012 (Dhahran)
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Constellations ???????

• Patterns of stars in the sky.
• 88 constellations.
• Served as a calendar.
• Some imagination.
• No physical relation
• between members
• of any constellation.

8
Zodiac circle of animals ????? ??????
9
Zodiac a band in which planets move.
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Motion of planets

• Follow the ecliptic.
• Retrograde motion apparent reverse of planets
  motion.

11
Motion of the Moon

• Follows the ecliptic in the sky.
• Moonrise is 50 min late every night.
• Moons shape changes because we see different
  amounts of its illuminated parts.

12
Eclipses

• The angle between the moons orbit to the
  ecliptic plane is 5.15.
• Eclipses do not occure every month.

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Eclipses

• Twice a year on average.
• New moon (Solar eclipse)
• Full moon (Lunar Eclipse)

14
2.1 Egyptian and Other Early Astronomy

• River Nile floods every summer.
• Relation to the first appearance of Sirius in
  the eastern sky before sunrise in early July.

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2.2 Greek Astronomy

• Prograde motion the ordinary direction of motion
  of planets (the same as the sun and the moon wrt
  stars).
• Retrograde motion the apparent backward motion
  of planets wrt to stars.
• Periods of retrograde motion ? Order of distance
  of planets

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2.2 Greek Astronomy

• Aristotle geocentric model

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2.2 Greek Astronomy

• Ptolemy epicycle, defernt, equant.

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Problems With the Geocentric Model

• The planets appear to change brightness, implying
  a change of distance.
• The planets undergo retrograde motion (they move
  backwards compared to the direction the Sun
  moves).
• Mercury and Venus are never seen at opposition
  (they always appear close to the Sun).

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2.2 Greek Astronomy

• Eratosthenes Measuring the diameter of Earth.

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